The Anatomy of Chlamydoselachus 441 



Garman (1885.2) states that in his (female) specimen of Chlamydoselachus the 

 "ureters" unite before reaching the cloaca, into which they empty by means of a single 

 aperture. From an inspection of his figure reproduced as my Text'figure 92, it appears 

 probable that the so'called ureters are large mesonephric ducts which unite before reaching 

 the single urethral opening. The fused portion may be considered a rudimentary urinary 

 sinus. 



Concerning the urinary sinuses of Chlamydoselachus, Hawkes (1907, p. 477), whose 

 observations were apparently made on a single specimen, writes : 



Each [urethral] aperture passes into an expanded chamber [U.S., my Text-figure 90a, 

 after Hawkes] with laminated walls, the lumen of which has a diameter of 5 mm. in the 

 cloacal region. The first portion of the sinus is imbedded in the thick cloacal walls. Each 

 sinus extends forward for a distance of 6 cm. beyond the cloaca along the inner side of the 

 kidney, but in front of this point it lies near the oviduct, at a distance from the kidney varying 

 from 1 to 2 cm. 



A survey of the specimens described to date indicates that paired urinary sinuses, 

 opening into the urogenital sinus by separate urethral apertures, are typical for the female 

 Chlamydoselachus. Nevertheless, there is marked variability. The rudimentary median 

 urinary sinus, or posterior fused portion of the mesonephric ducts, described by Garman, 

 is anomalous. It illustrates one method by which a single median bladder, opening by 

 a single urethral aperture, might be evolved. In my specimens, I find two instances 

 (Text'figures 91a and b) where the right urinary sinus is smaller than the left, and one 

 instance (Text'figure 91c) where the right urinary sinus is irregular in shape. In two 

 instances (specimens IV and III) a right urethral aperture could not be found, while in 

 two others (Nos. I and II) the right urethral aperture is smaller than the left. In No. Ill 

 no connection of the right urinary sinus with a mesonephric duct could be found. To 

 offset these deficiencies of the right urinary sinus and its openings there is but one instance 

 of similar deficiency on the left side: in No. II a probe could not be passed from the left 

 urinary sinus into the left mesonephric duct, though the latter is of normal si^e. It is 

 evident that the urinary sinus and also the urethral pore of the right side are much more 

 likely to be defective. That genetic factors are involved is probable from the condition 

 in specimen No. IV, which is quite immature, and in No. Ill, which is not fully mature. 



In Heptanchus maculatus (Daniel, 1934) there is ordinarily a single median urinary 

 sinus, but in one specimen two urinary sinuses, right and left respectively, were found. 

 I have been unable to find any other instances, except in Chlamydoselachus, of a pair of 

 urinary sinuses opening separately into the urogenital sinus of an elasmobranch. In the 

 Myxinidae, the mesonephric ducts are said (Sedgwick, 1905) to open separately into the 

 urogenital sinus, but in Petromyzon these ducts join to discharge their fluid through 

 a single pore. In vertebrate embryos, the mesonephric ducts open separately. The 

 condition found in Chlamydoselachus is probably primitive in a phylogenetic sense, 

 but may be due to arrested development. 



